Method of preventing oxidation of spark plug shell plating by thermoplastic sealing



June 20, 1967 R BRUMBACK, 3,327,087

METHOD OF PREVENTING OXIDATION OF SPARK PLUG SHELL PLATING BY THERMOPLASTIC SEALING F'iled Sept. 21, 1964 T0 POWER SUPPLY TO POWER SUPPLY INVENTOR. WILLSON P. BRUMBACK JR.

v ATTOR EYS United statesPatcn O.

METHOD OF PREVENTING OXIDATION OF SPARK PLUG SHELL PLATING BY THER- MOPLASTIC SEALING Willson P. Brumback, Jr., Decatur, Ala., assignor to Eltra Corporation, Toledo, Ohio, a corporation of New York Filed Sept. 21, 1964, Ser. No. 397,978 1 Claim. (Cl. 219-72) This invention relates to spark plugs and more particularly to a method of protecting the plating during the hot pressing operation for spark plug shells.

The invention contemplates a method of protecting the bright electroplated coating on spark plug shells for decorative purpose during the hot press sealing operation for spark plug shells which will eliminate discloloration of that portion of the plated shell which is heated to plasticity during the hot press" operation.

The hot press method of sealing spark plug shells has long been used in the mass production of spark plugs and is disclosed in U.S. Patent No. 2,111,916. When shells are electroplated before hot press sealing operation to improve their appearance to enhance their saleability, a dark ring is produced by the heating with oxidation of the plating in and around the hot press area. The present invention contemplates the provision of a cheap and effective method of hot press sealing which prevents the oxidation of the electroplated outer surface of the shell at the heated zone to thereby enhance the appearance of the final spark plug and improve its acceptance in the market place.

It is therefore a principal object of this invention to provide a method of producing a spark plug which has an electroplated shell for decorative purposes that can be sealed in a hot press operation without oxidation or discoloration of the plasticized area of the plated shell.

It is another object of this invention to provide a cheap and effective method of hot pressing electroplated spark plug shells which will prevent oxidation and discoloration of the decorative plating on the exterior of the shell.

Other objects and advantages of this invention relating to the arrangement, operation and function of the related elements of the structure, to various details of construction, to combinations of parts and to economies of manufacture will be apparent to those skilled in the art upon consideration of the following description and appended claim, reference being had to the accompanying drawings forming a part of this specification wherein like reference characters designate corresponding parts in the several views.

Referring to the drawings:

FIG. 1 is a sectional elevation of a portion of a hot press mechanism incorporating mechanisms for carrying out the method of the invention; and

FIG. 2 is a view similar to FIG. 1 showing the mechanism performing a hot press sealing operation of a spark plug.

In the drawings, a conventional hot press mechanism is shown which has been adapted to include the invention. A lower die member 12 is shown which is suitably mounted on a stationary base 14, and an upper movable die member 16 which cooperates with the lower die member as shown during a hot press" operation. The lower die member 12 is provided with a cavity 12a in which a spark plug is positioned by the operator in alignment with a cavity 16a provided in the upper die 16. An annular planar surface 12b surrrounding the cavity 12a provides a bearing surface for the spark plug shell and prevents downward movement of the plug during the pressing operation. The cavity 16a includes an annular recess 16b which conforms to an annular turned in flange ice [portion 18 of a spark plug shell 20 which is turned in as a preparatory step to the hot press step. During a hot press operation, the upper die is lowered to contact the flange 18 of the shell 20, as shown in FIG. 2 to apply downward pressure thereto, prior to the closing of the electrical power circuit by conductors 24 and 26 which causes an electric current to fiow through the shell be-,

tween the die portions to cause heating of the attenuated annular portion to plasticity. This process is old in the art and is disclosed in Patent No. 2,111,916 mentioned hereinbefore.

The invention is concerned primarily with the area 22 of the spark plug shell which is attenuated to heat it to plasticity to allow the hot press to occur. It should be noted that the location of this thermoplastically collapsed section on the shell must be between the shoulders on the insulator (not shown) to allow compression to be applied to gaskets when the spark plug cools. The hot press section 22 is the annular area in which the electroplating on the spark plug shells is oxidized by the heating to cause the electroplating to darken in this section during the hot press operation. It has been discovered that if the spark plug shell is submerged in a suitable cooling liquid such as water, the presence of the liquid will maintain the temperature at the electroplating sufficiently low to prevent oxidation of the plating. The circumambient liquid also tends to cool the plating surface while allowing the thermoplastically collapsed section of the shell to reach the proper temperature to provide a good hot press seal for the spark plug. The discoloration of the spark plug shell is reduced by the submersion by reducing the amount of free oxygen reaching the plated surface during the period of high temperature.

This submerging operation is carried out in a mass production line for spark plugs by permanently mounting a suitable container 30 on the lower die 12 surrounding the spark plugs positioned in the cavity 12a which will contain a cooling liquid such as water 33. A hole 32 is provided in the bottom of the container which is slightly larger than the diameter of the cavity 12a providing sufficient clearance to position the spark plug in the die. A suitable seal such as a weld is provided around the hole 32 to prevent escape of the liquid 33 from the container. The container also has suitable couplings 34 which provide inlet and/or outlet passages, as the case may be, for supplying or exhausting liquid in the container, the position of the couplings provide a ready means to control the level of the cooling liquid in the container 30. In a hot press operation (FIG. 2), the electroplated spark plug S is inserted in the cavity 12a in the lower die in subassembled state wherein gaskets have been provided and the flange 18 rolled in. The container 30 is filled with water 33 to a level to reach approximately to the top of the shell. When the upper die member 16 is applying a predetermined pressure to the shell, current is applied in the conventional manner which heats the shell to thermoplasticity at section 22 sufiicient to collapse it after which the upper die is raised to remove the pressure. This completes a hot press sealing cycle and the spark plug is removed from the lower die 12 by the opera tor. In the development of this process, liquids other than water were used and have been found satisfactory but not as economical.

The temperature of the outer surface of section 22 by the presence of the cooling liquid is prevented from rising to such values to cause oxidation of the outer surface electroplating, whereby a spark plug is provided which is decoratively enhanced to improve its saleability in the market place. The electroplating may be nickel, cadmium, zinc or any other metal or combination of metals found desirable.

It is to be understood that the above-detailed description of the present invention is intended to disclose an embodiment thereof to those skilled in the art, but that the invention is not to be construed as limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings since the invention is capable of being practiced and carried out in various ways without departing from the spirit of the invention. The language used in the specification relating to the operation and function of the elements of the invention is employed for purposes of description and not of limitation, and it is not intended to limit the scope of the following claim beyond the requirements of the prior art.

What is claimed:

The method of improving the appearance of a spark plug sealed by thermoplastically collapsing an annular section of the tubular shell, comprising providing the shell with an electroplated metal layer on its outer surface, heating the annular section of the shell to a condition of thermoplasicity by an electric current, maintaining the temperature of the electroplated metal layer on the outer surface of the thermoplastic annular section sufficiently low by immersion of the spark plug in a cooling liqlid to prevent oxidation and discoloration, and collapsing the section by longitudinal pressure when the condition of thermoplasticity is reached to seal the spark plug.

References Cited UNITED STATES PATENTS 1,193,075 8/1916 Schmidt 29511 X 1,691,522 11/1928 Kobert 219150 1,862,981 6/ 1932 Rabezzana 29511 X 1,888,413 11/1932 Sebell 29458 X 2,111,916 3/1938 Middleton 29511 X 2,308,968 1/1943 Gregory.

2,412,271 12/1946 Kercher 29458 X CHARLIE T. MOON, Primary Examiner. 

